UNIVERSITY    OF    CALIFORNIA     AGRICULTURAL    EXPERIMENT  STATION 

BENJ.    IDE    WHEELER,    PRESIDENT 
THOMAS    FORSYTH    HUNT,    Dean  and  UirectoK 
BERKELEY  H.    E.    VAN    NORMAN,    vice-director    ano    Dean 

University  Farm   School 


COLLEGE   OF  AGRICULTURE 


CIRCULAR  No.  181 

November,  1917 

CONTROL  OF  THE  CALIFORNIA 
GROUND  SQUIRREL 

By  JOSEPH  DIXON 

(Contribution  from  the  Museum  of  Vertebrate  Zoology  of  the  University  of  California) 


The  ground  squirrels  are  undoubtedly  the  most  widely  known 
and  at  the  same  time  the  most  disliked  mammals  in  California.  The 
large,  long-tailed,  grayish-brown  species  known  as  the  California  or 


Fig.  1  .^Diagram  showing  methods  of  destroying  ground  squirrels  to  be  employed 
at  different  seasons  of  the  year. 


"digger"  squirrel  (Citellus  beecheyi  and  subspecies)  is  of  chief  im- 
portance in  its  relation  to  man;  first,  because  of  its  destructiveness 
to  crops ;  second,  because  it  is  a  carrier  of  disease ;  and  third,  because 
of  the  damage  done  by  it  to  irrigation  works. 

Three  races  of  the  digger  squirrel  occur  within  the  state :  the 
dark-colored  northern  form  (the  Douglas  ground  squirrel)  which 
ranges  from  San  Francisco  Bay  northward  throughout  that  portion 
of  the  state  which  lies  west  and  north  of  the  Sacramento  •  and  Feather 
rivers;  the  brownish  Beechey  ground  squirrel  which  occupies  central 
California  and  the  coast  district  south  from  the  Golden  Gate;  and 
the  gray-toned  Fisher  ground  squirrel  whose  habitat  lies  in  the  south- 
ern San  Joaquin  and  Owens  valleys  and  to  the  south  throughout 
southern  California.  The  characters  which  serve  to  distinguish  these 
different  races  are  not  of  any  particular  importance  in  relation  to  the 
work  of  eradicating  these  pests,  so  that  from  this  standpoint  the  three 
forms  may  be  considered  as  one.  A  knowledge  of  certain  habits  of 
feeding,  breeding  and  hibernation  possessed  by  these  animals  is  of 
the  greatest  importance  in  control  work  and  these  habits  are  con- 
sidered at  some  length  in  the  following  pages. 


NATURE  AND    EXTENT   OF   DAMAGE 

According  to  Dr.  C.  Hart  Merriam,  of  the  United  States  Biological 
Survey,  the  national  loss  to  agriculture  through  depredations  of 
ground  squirrels  amounts  to  at  least  10  million  dollars  annually.  No 
other  state  suffers  more,  or  as  much,  in  this  regard,  as  California. 
The  loss  due  to  the  ground  squirrel  in  California  alone  has  been  placed 
at  as  high  a  figure  as  that  given  above  for  the  entire  country,  so  that 
it  is  a  conservative  estimate  to  put  the  annual  loss  due  to  ground 
squirrels  in  this  state  as  not  less  than  five  million  dollars. 

The  California  ground  squirrel  occurs  in  troublesome  numbers  in 
most  of  the  best  farming  and  fruit-raising  districts  of  the  state.  It 
is  a  voracious  feeder  and  reproduces  rapidly.  Practically  all  kinds 
of  grain  and  many  kinds  of  fruit  are  subject  to  its  depredations. 
This  squirrel  prefers  an  elevated  location  for  its  homesite,  and  in 
digging  burrows  it  often  honeycombs  the  banks  of  irrigation  ditches, 
with  disastrous  results. 

.The  ground  squirrel  is  a  carrier  and  disseminator  of  bubonic 
plague.  Between  May,  1907,  and  September,  1912,  over  1000  plague- 
infected  ground  squirrels  were  examined  from  a  single  county  in  the 
San  Francisco  Bay  region  by  the  United  States  Public  Health  Ser- 
vice.     While  the  immediate  danger  of  acquiring  the  plague  through 


ground  squirrels  seems  to  have  largely  passed,  their  destruction  would 
surely  tend  to  prevent  the  recurrence  of  danger  on  this  score. 

FEEDING    HABITS 

California  ground  squirrels  have  membranous  cheek-pouches  which 
open  inside  the  mouth  and  are  used  to  carry  food,  principally  grain, 
to  the  underground  store  rooms.  These  cheek-pouches  are  not  lined 
with  fur  as  are  those  of  the  pocket  gopher,  but  have  thin  walls  which 
readily  absorb  the  strychnine  on  the  outside  of  poisoned  grain.  It 
has  been  demonstrated  that  ground  squirrels  are  more  readily  poisoned 
through  these  cheek-pouches  by  merely  carrying  poisoned  grain,  than 
through  the  stomach  after  they  have  eaten  it.  For  this  reason  the 
coated  grain  is  preferred  to  that  which  has  been  soaked  in  a  strychnine 
solution. 

The  food  and  feeding  habits  of  ground  squirrels  vary  greatly  with 
the  locality  and  season  of  the  year.  During  the  rainy  season,  from 
November  to  April,  although  they  utilize  some  grain,  seeds  or  nuts 
that  have  been  stored  up  during  the  previous  summer,  their  main 
reliance  is  upon  grass  and  other  green  herbage.  This  results  in  a 
very  serious  loss  in  many  localities,  as  it  greatly  reduces  the  pasturage 
available  for  horses  and  cattle.  "When  green  stuff  is  abundant,  com- 
paratively little  food  is  carried  in  the  cheek-pouches.  However,  by 
the  last  of  March  certain  plants,  such  as  alfilaria,  have  begun  to  go 
to  seed,  and  the  squirrels  then  begin  to  use  their  cheek-pouches  exten- 
sively in  harvesting  these  seeds.  At  this  time  the  squirrels  take  the 
poisoned  grain  readily,  but  later  in  the  season  when  the  cultivated 
grain  begins  to  ripen  they  are  much  harder  to  poison  on  account  of 
the  abundant  grain  supply  then  available. 

Ground  squirrels  are  very  fond  of  the  soft  pits  of  peaches,  almonds 
and  apricots,  and  in  getting  these  they  destroy  much  fruit.  On  the 
whole,  however,  the  principal  loss  from  ground  squirrels  is  in  the 
grain  fields,  where  the  animals  dig  up  and  destroy  the  sprouting  seed 
and  later  pull  down  and  destroy  a  vast  amount  of  the  ripening  grain. 
After  the  crops  are  harvested  they  congregate  about  the  shocks  and 
stacks  and  continue  to  devour  and  carry  off  quantities  of  grain.  At 
this  time  watermelon  rinds  poisoned  with  strychnine  are  extremely 
effective,  since  succulent  green  food  is  scarce. 

AESTIVATION    OF  THE   GROUND    SQUIRREL 

There  is  evidence  to  support  the  belief  that  a  period  of  aestivation, 
or  state  of  torpidity  induced  by  the  heat  and  dryness  of  summer, 
obtains  among  some  of  the  adult  ground  squirrels  in  the  valleys  of 


California.  This  period  of  dormancy  extends  from  late  summer  well 
through  midwinter,  and  thus  involves  hibernation  as  well  as  aestiva- 
tion. The  old  adults  seem  to  be  the  only  ones  that  ' '  hole  up, ' '  for  the 
young  adults  (somewhat  over  a  year  old)  and  the  young  of  the  year 
may  be  seen  about  the  burrows  during  suitable  weather  throughout 
the  winter.  A  close  and  continuous  watch,  extending  "over  several 
years,  was  kept  on  a  female  ground  squirrel  that  lived  under  normal 
conditions  in  the  dooryard  at  the  home  of  Mrs.  Elizabeth  Grinnell  in 
Pasadena.  These  observations  brought  forth  the  following  facts. 
This  particular  squirrel  did  not  aestivate  until  its  second  year.  Then 
and  during  each  succeeding  year  of  its  life  it  aestivated  regularly, 
becoming  very  fat  and  retiring  to  its  burrow  during  the  last  week  in 
August.  The  squirrel  emerged  in  an  emaciated  condition,  with 
marked  regularity,  about  the  22nd  of  each  following  February.  When 
removed  from  the  burrow  during  this  period,  this  animal  was  found 
to  be  in  a  torpid  state  and  respiration  was  not  perceptible.  This  habit 
of  aestivation  affords  explanation  of  a  case  in  the  author's  experience, 
in  which  all  the  squirrels  that  were  active  in  a  certain  field  in  the  fall 
were  poisoned  or  killed,  and  yet  old  breeding  squirrels  suddenly 
appeared  in  this  same  field  the  following  February.  This  state  of 
affairs  occurred  when  there  was  seemingly  no  possible  chance  for 
re-infestation  from  the  surrounding  fields.  The  extent  of  this  habit 
of  aestivation  among  our  ground  squirrels  is  unknown.  It  is  ex- 
ceedingly difficult  to  follow  any  individual  squirrel  through  all  its 
various  activities  for  any  great  length  of  time.  However,  an  im- 
portant factor  concerned  in  the  work  of  destroying  these  animals  is 
suggested;  that  is,  the  desirability  of  placing  emphasis  upon  the  need 
of  poisoning  in  the  spring  rather  than  in  the  fall  when  some  of  the 
breeding  stock  may  be  stowed  away  out  of  the  reach  of  poisoned  grain. 
It  is  a  question,  too,  whether  or  not  a  dormant  animal,  in  which 
respiration  is  extremely  slow,  would  be  fatally  injured  by  a  fumigant 
before  the  latter  would  disappear. 

TIME   AND    RATE   OF   BREEDING 

The  accompanying  chart  (fig.  2)  is  based  on  over  10,000  female 
squirrels  examined  by  the  United  States  Public  Health  Service  during 
the  spring  and  summer  of  1910,  and  proves  that  the  California  ground 
squirrel  has  a  very  definite  breeding  season  and  that  this  period  begins 
about  the  first  of  February  and  lasts  until  the  first  of  May.  The 
maximum  number  of  pregnant  females  was  found  during  the  week 
ending  February  26.  The  bulk  of  the  young  are  born  about  five 
weeks  after  this  date  and  may  be  seen  running  about  at  the  entrances 


of  the  burrows  a  month  or  six  weeks  after  they  are  born.  In  low, 
warm  valleys  the  breeding  season  has  been  found  to  be  somewhat 
earlier  than  the  above  averages  would  indicate,  while  along  the  coast 
and  in  the  mountains  the  breeding  season  is  about  two  weeks  later 
than  the  dates  given. 

The  usual  annual  increase  of  a  pair  of  ground  squirrels  consists  of 
one  litter  of  from  five  to  eleven  young.  The  average  number  of 
embryos  in  pregnant  females  was  found  by  the  United  States  Public 


Jan. 

Feb. 

Mar. 

Apr. 

moy 

AZ 
10 
36 

36 
34 
32 
30 
26 
26 
24 
22 
20 
16 
16 
14 
IZ 
10 
8 
6 
4 
2 
0 

22 

29 

5 

-iZ 

/9       2 

6       6 

12 

19 

26 

2. 

9 

/6 

23 

30 

7 

14 

:r 

1 

k 

it 

\ 

iA 

1 
I 

\ 

t 

/ 

\ 
\ 

i 

t 

\ 

*" T 

\ 

i 

\ 

J 

\ 

i 

\ 

/ 

\ 

^ 

i 

" 

■»<, 

/ 

[S 

i 
I 

■»% 

/ 

i 

\ 

_£ 

/ 

/ 

\ 

f 

/ 

\ 

\ 

/ 

i 

\ 

\ 

* 

' 

i 

\ 

\ 

i 

\ 

I 

i 

\ 

/ 

k-- 

\^_ 

/ 

i 
i 

^ 

N 

\ 

f 

i 

\ 

Fig.  2. — Chart  showing  breeding  season  of  California  ground  squirrels.  (Com- 
piled chiefly  from  data  obtained  from  United  States  Public  Health  Eeports,  vol. 
27,  July  5,  1917,  p.  1070.)  Figures  in  left-hand  column  represent  per  cent  of 
females  found  pregnant;  over  10,000  females  examined.  Eepresents  preva- 
lence of  pregnacy  among  female  ground  squirrels  between  January  15  and  May  14. 
For  example,  during  the  week  ending  March  5,  27  per  cent  of  females  examined 

were  pregnant.     Shows  approximately  the  time  of  birth  of  the  bulk  of  young 

squirrels. 


Health  Service  to  be  7.2.  There  is  some  evidence  to  indicate  that 
a  second  litter  is  sometimes  raised  in  a  single  season,  but  this  is  surely 
not  the  usual  thing  The  important  point  to  be  noted  in  this  connec- 
tion is  that  one  breeding  female  killed  before  April  1,  that  is,  before 
the  young  are  able  to  take  care  of  themselves,  is  equal  to  the  destruc- 
tion of  from  six  to  twelve  squirrels  later  in  the  season.  A  wise  man 
will  go  after  the  squirrels  early  in  the  year,  when  "a  stitch  in  time" 
will  literallv  "save  nine." 


METHODS  OF  CONTROL 

The  five  most  effective  methods  of  destroying  ground  squirrels  are : 
(1)  poisoning  with  strychnine;  (2)  fumigation  with  carbon  bisul- 
phide; (3)  trapping;  (4)  shooting;  (5)  encouragement  of  the  natural 
enemies  of  the  ground  squirrel. 

WHICH    METHOD  TO    USE,   WHEN,   AND   WHY 

(See  Fig.  1) 
i.  Carbon   bisulphide   is   most   effective   when   the   soil   is   damp. 
When  the  ground  is  dry  the  gas  escapes  through  the  cracks  in  the 
ground. 

2.  Strychnine-coated  barley  is  best  used  during  the  dry  season 
because  at  this  time  the  squirrels  gather  and  store  grain  and  hence 
are  easily  poisoned  through  their  cheek  pouches  when  in  the  act  of 
carrying  the  poisoned  grain.  Rain  and  heavy  fogs  tend  to  wash  the 
strychnine  off  the  poisoned  grain. 

3.  Trapping  and  shooting  are  effective  at  any  time,  but  are  from 
six  to  twelve  times  more  so  before  the  young  are  out,  before  April  1, 
than  later  in  the  season. 

4.  Powdered  strychnine  (sulphate)  in  fresh  vegetables  and  fruit 
is  especially  effective  in  the  dry  season  when  green  food  is  scarce. 

5.  Red-tailed  hawks,  Golden  eagles,  badgers,  weasels,  and  other 
natural  enemies  of  the  ground  squirrel  will  prove  valuable  allies  in 
the  war  on  ground  squirrels  if  they  are  only  allowed  to  live.  It  costs 
little  to  let  them  alone,  to  go  about  their  business  in  the  natural  way. 

COMPARATIVE    COST    OF   VARIOUS    METHODS 

In  1910,  Dr.  C.  Hart  Merriam1  gave  the  cost  of  one  treatment 
with  poisoned  grain  as  3  cents  per  acre  and  for  one  treatment  with 
carbon  bisulphide   ("waste-ball"  method)   at  iy2  cents  per  burrow. 

In  1912,  Surgeon  John  D.  Long2  put  the  cost  of  the  various 
methods  of  destruction,  with  carbon  bisulphide  at  90  cents  per  gallon, 
as  follows;  cost  per  acre,  estimated  on  the  basis  of  ten  holes  per  acre. 

Carbon  bisulphide,  with  "destructor"   (two  treatments)  $  .20 

Poisoned  grain    (four  or  five  treatments)  35 

Carbon  bisulphide,  waste-ball  method  (two  treatments) 68 

Surgeon  Long  reports  that  in  actual  practice  one  gallon  of 
bisulphide  would  treat  from  200  to  250  holes  when  used  with  the 
"destructor"  and  from  50  to  60  holes  when  used  per  the  waste-ball 
method. 

i  Merriam,  C.  II.     U.  S.  Dept.  Agric,  Biological  Survey,  Circular  no.  76,  1910. 
2  Long,  J.  D.     United  States  Public  Health  TCeports,  vol.  27,  no.  39,  September 
27,  1912. 


Crude  carbon  bisulphide  is  still  quoted  (August,  1917)  at  90 
cents  a  gallon,  in  live-gallon  lots  in  San  Francisco,  but  strychnine 
has  advanced  to  $1.35  per  ounce  for  the  sulphate  and  $1.60  per  ounce 
for  the  alkaloid  form.  Ammunition  has  nearly  doubled  in  price, 
so  that  the  present  cost  of  the  various  methods  of  destroying  ground 
squirrels  is,  on  the  average,  considerably  higher  than  Surgeon  Long's 
estimate,  which  latter  seems  to  be  the  best  and  most  accurate  thus  far 
published  on  the  subject,  both  as  to  the  number  of  treatments  required 
and  as  to  the  relative  cost. 

(1)   POISONING  WITH  STRYCHNINE 

Barley  as  a  vehicle  for  the  poison  is  usually  more  attractive  to  the 
ground  squirrel  than  wheat.  It  is  also  less  likely  to  be  eaten  by  birds, 
stock  and  poultry.  Hence  barley  should  be  used  for  this  purpose 
instead  of  wheat.  Care  should  always  be  taken  not  to  leave  more 
than  a  teaspoonful  of  poisoned  grain  in  a  place  and  it  should  never 
be  left  where  poultry  can  pick  it  up.  The  alkaloid  form  of  strychnine 
is  only  slightly  soluble  in  water  and  is  considered  the  best  form  to 
use  in  preparing  poisoned  barley  for  the  reason  that  it  is  not  so 
easily  affected  by  fog  and  rain.  When  gathered  and  placed  in  the 
cheek-pouches  by  the  ground  squirrel,  the  strychnine-coated  barley 
often  gets  in  its  deadly  work  before  the  animal  has  a  chance  to  detect 
the  bitter  taste  of  the  strychnine  and  reject  the  poisoned  grain. 

Formula  for  Strychnine-coated  Barley. — Following  is  the  latest 
government  formula3  for  preparing  poisoned  barley  for  California 
ground  squirrels. 

Barley    (clean  grain)  16  quarts 

Strychnine    (powdered   alkaloid) 1  ounce 

Bicarbonate  of  soda  (baking  soda)  1  ounce 

Thin  starch  paste %  pint 

Heavy  corn  sirup %  pint 

Glycerin 1  tablespoonful 

Saccharin ]/io  ounce 

Mix  thoroughly  1  ounce  of  powdered  strychnine  (alkaloid)  and  1  ounce  of 
common  baking  soda.  Sift  this  into  %  pint  of  thin,  hot  starch  paste  and  stir  to 
a  smooth,  creamy  mass.  (The  starch  paste  is  made  by  dissolving  1  heaping  table- 
spoonful  of  dry  gloss  starch  in  a  little  cold  water,  which  is  then  added  to  %  pint 
of  boiling  water;  boil  and  stir  constantly  until  a  clear,  thin  paste  is  formed.) 
Add  %  pint  of  heavy  corn  sirup  and  1  tablespoonful  of  glycerin  and  stir  thor- 
oughly. Add  y10  ounce  of  saccharin  and  stir  thoroughly.  Pour  this  mixture  over 
16  quarts  of  clean  barley  and  mix  well  so  that  each  grain  is  coated. 

Caution.-*-A\l  containers  of  poison  and  all  utensils  used  in  the  preparation  of 
poisons  should  be  kept  PLAINLY  LABELED  and  OUT  OF  BEACH  of  children, 
irresponsible  persons,  and  live  stock. 

3  Circular  letter  issued  by  Bureau  of  Biological  Survey,  U.  S.  Dept.  Agric. 
June,  1917. 


8 

Placing  Poisoned  Grain. — The  poisoned  barley  should  be  well 
scattered  over  clean  hard  ground  near  the  holes.  Squirrel  paths  that 
lead  along  fences  or  to  or  from  the  dens  are  good  places  in  which  to 
scatter  the  grain.  Poisoned  grain  will  be  largely  wasted  if  dropped  in 
thick  grass  or  in  dusty  places.  It  will  also  often  be  covered  up  if  left 
on  the  loose  dirt  at  the  entrance  to  the  burrow. 

Poisoning  Fresh  Fruits  and  Grain. — Strychnine  sulphate  is  freely 
soluble  in  fruit  juices  and  these  seem  to  conceal,  to  some  degree  at  least, 
the  bitterness  of  the  strychnine.  Some  of  the  best  results  in  the 
writer's  experience  in  poisoning  squirrels  were  secured  with  oranges 
cut  in  halves  which  were  then  sprinkled  with  powdered  strychnine  and 
left  in  paths  of  the  squirrels.  Watermelon  rinds  often  prove  very 
effective  if  cut  into  pieces  as  large  as  one's  hand  and  poisoned  by 
sprinkling  with  powdered  strychnine.  Green  barley  heads  in  the 
"dough"  stage,  with  the  beards  clipped  off,  have  been  found  very 
deadly  if  soaked  for  fifteen  or  twenty  hours  in  a  solution  of  one  ounce 
of  strychnine  sulphate  to  a  gallon  of  water.  The  solution  should  be 
brought  to  a  boil  and  then  allowed  to  cool  before  the  barley  is  put  in. 
It  is  wise  to  take  every  precaution  in  placing  these  baits  so  as  to  put 
them  in  protected  places,  such  as  rockpiles,  where  there  is  no  chance 
for  stock  to  reach  them;  and  it  is  also  advisable  to  thoroughly  wash 
one's  hands  immediately  after  putting  out  the  poisoned  bait. 

(2)  FUMIGATION  WITH  CAEBON  BISULPHIDE 
Carbon  bisulphide  gas  is  one  of  the  best  agents  for  destroying 
those  ground  squirrels  that  have  failed  to  take  the  poisoned  grain  or, 
having  once  survived  the  poison,  refuse  to  take  it  again.  The  follow- 
ing facts  should  be  kept  in  mind  regarding  the  use  of  carbon  bisul- 
phide, (a)  The  gas  from  carbon  bisulphide  is  highly  inflammable 
and  it  should  be  kept  away  from  all  fires  and  exposed  lights.  (b) 
Being  heavier  than  air,  this  gas  settles  in  the  lowest  places  in  the 
underground  burrow  and  hence  will  not  go  over  an  elevation  higher 
than  the  entrance  of  the  burrow  unless  an  "exterminator"  or  "de- 
structor" is  used  to  forcibly  pump  the  burrow  full  of  gas  or  unless 
the  gas  is  exploded  in  the  burrow.  (c)  When  the  ground  is  dry  and 
full  of  cracks  the  gas  escapes  and  is  not  nearly  as  effective  as  if 
used  when  the  ground  is  wet  and  the  gas  therefore  confined  to  the 
burrow,  (d)  It  should  be  used  only  in  holes  that  are  known  to  be 
occupied  by  squirrels  at  the  time  of  the  treatment,  '(e)  Carbon 
bisulphide  should  be  kept  tightly  corked  as  it  loses  strength  rapidly 
on  exposure  to  the  air. 

The  two  best  methods  of  applying  carbon  bisulphide  are  by  the 


use  of  the  "waste-ball"  method  and  of  the  "destructor."  The  com- 
mon waste-ball  method  is  to  pour  a  tablespoonful  of  carbon  bisulphide 
on  a  piece  of  cotton  waste,  corncob,  horse  manure,  or  other  absorptive 
material,  which  should  then  be  thrown  as  far  down  the  hole  as  possible 
and  the  opening  immediately  closed  with  earth. 

Exploding  the  Gas. — The  explosion  of  the  gas  in  connection  with 
the  waste-ball  method  is  recommended  where  the  ground  is  damp  and 
there  is  no  danger  from  fire.  When  the  bisulphide  gas  in  a  burrow 
is  exploded  two  new  gases  (carbon  monoxide  and  sulphur  dioxide) 
are  formed,  both  poisonous.  These  diffuse  somewhat  more  rapidly 
and  pass  more  readily  over  elevations  than  bisulphide  and  penetrate 
to  the  very  ends  of  all  branches  of  the  burrow.  A  "destructor" 
should  be  used  in  grain  fields  or  in  other  places  where  there  is  danger 
from  fire,  since  by  its  use  the  burrow  is  pumped  completely  full  of 
the  carbon  bisulphide  gas  and  hence  the  explosion  of  the  gas  becomes 
unnecessary. 

A  six-foot  piece  of  14-inch  pipe  with  one  end  closed  and  pointed 
and  the  other  end  tightly  wrapped  with  a  rag  soaked  in  coal  oil  adds 
safety  to  the  operation  of  exploding  the  gas  in  the  burrow.  After 
the  bisulphide  has  been  confined  in  the  burrow  for  a  few  seconds, 
a  hole  is  made  with  the  pointed  end  of  the  pipe  through  the  dirt  plug 
at  the  entrance  of  the  burrow.  The  gas  is  then  "touched  off"  wTith 
the  torch,  which  has  been  previously  lighted,  on  the  other  end  of  the 
rod.  It  is  advisable  to  stand  well  to  one  side  of  the  burrow  when 
doing  this. 

The  second  system  of  applying  carbon  bisulphide  has  been  used 
by  Passed  Assistant  Surgeon  John  D.  Long  of  the  U.  S.  Public  Health 
Service,  who  devised  a  simple  "destructor"  which  pumps  the  vapor- 
ized bisulphide  into  the  burrow.4  Laboratory  experiments  showed 
that  the  animal  is  but  little  alarmed  by  the  gas  and  makes  no  effort 
to  escape  or  to  seek  fresh  air.  In  ten  or  fifteen  minutes  after  the 
gas  is  pumped  into  the  burrow  the  animal  falls  over  and  in  from 
thirty  to  forty-five  minutes  is  dead. 

This  destructor  (fig.  3)  is  composed  principally  of  18-gauge  galvanized  iron. 
The  circular  top,  bottom  and  piston  are  made  from  veneered  wood  so  as  to  prevent 
warping  or  splitting.  Stated  simply,  the  main  parts  of  this  apparatus  are  as 
follows:  An  air  chamber  (1),  containing  the  piston  (10),  is  entirely  surrounded 
by  the  bisulphide  tank  (2).  This  tank  is  connected  with  the  vaporizing  chamber 
(4)  through  the  measuring  cup  (15).  In  operating  the  destructor,  a  short  rubber 
hose  connected  to  the  outlet  (17)  is  inserted  at  least  one  foot  into  an  occupied 
squirrel  burrow  and  tightly  surrounded  with  dirt.      Then  the  three-way  cock  (16) 


*  Long,  J.  D.     United  States  Public  Health  Reports,  vol.  27,  no.  39,  Septembei 
27,  i.912. 


10 

is  turned  so  that  the  measuring  cup  (15)  is  filled  with  y2  ounce  of  refined 
bisulphide,  which  is  permitted  by  another  turn  of  the  cock  to  run  into  the 
vaporizing  chamber  (4). 

The  pump  has  a  double  action,  for  air  is  admitted  at  the  proper  time  at  the 
inlet  valves  (7)  at  both  the  top  and  the  bottom  of  the  cylinder  when  the  piston 
(10)  is  worked  up  and  down  by  the  handle  (14).  The  air  thus  compressed  escapes 
through  the  outlet  valves  (8)  into  the  air  shaft  (9),  which  in  turn  conveys  it  to 
the  vaporizing  chamber  (4).  From  the  vaporizing  chamber  the  bisulphide  gas 
is  forced  into  the  burrow  through  a  rubber  hose  connecting  with  the  outlet  (17). 
Fifteen  double  strokes  of  the  pump  forces  12  cubic  feet  of  1.5  per  cent  bisulphide 
gas  down  the  squirrel  burrow;  this  is  sufficient  to  kill  the  animal.  The  rubber 
hose  is  then  withdrawn  from  the  burrow  and  the  hole  closed  by  stamping  in  the 
dirt  with  the  heel  of  one's  shoe. 

This  destructor  has  been  placed  on  the  market  through  a  San 
Francisco  firm.  The  Eureka  Squirrel  Exterminator  and  other  sim- 
ilar machines  operate  on  principles  similar  to  that  of  the  destructor 
just  described,  while  a  rancher  of  mechanical  turn  of  mind  should  be 
able  to  construct  a  machine  for  the  most  part  out  of  an  old  brass 
cylinder  and  other  materials  from  the  scrap  pile  to  be  found  about 
the  average  ranch. 

(3)   TKAPPING;    (4)   SHOOTING 

Where  ground  squirrels  are  digging  into  ditch  banks,  and  in 
similar  cases  where  they  must  be  disposed  of  promptly  at  any  cost, 
special  means  of  getting  rid  of  them  must  be  adopted.  Trapping 
and  shooting  are  two  valuable  methods  of  control  for  such  local  appli- 
cation. While  these  two  methods  can  be  used  at  any  season,  the  time 
required  to  keep  the  traps  properly  set,  which  is  essential  to  success, 
and  the  high  initial  cost  of  the  traps  as  well  as  the  present  high  cost 
of  ammunition  make  them  too  expensive  for  general  use  on  large  acre- 
age. Trapping  and  shooting  are  worth  while  in  cleaning  up  the  few 
wise  squirrels  which  escape  the  poison  and  carbon  bisulphide,  and  in 
reducing  the  breeding  stock  in  the  early  spring  before  the  annual 
five-fold  increase. 

The  No.  1  Oneida  jump  trap  is  the  best  trap  to  use,  as  it  is  lighter, 
easier  to  set,  and  has  a  larger  catching  surface  (pan  or  treadle)  than 
the  ordinary  steel  trap  with  the  outside  spring.  The  jump  trap  lies 
flat  on  the  ground ;  the  jaws  have  wide  contact  surfaces  which  reduce 
the  chance  of  breaking  the  animal's  leg;  and  the  construction  of  the 
inside  spring  causes  the  trap  to  jump  up  and  take  a  high  grip  on  the 
leg  instead  of  on  the  foot  only.  Such  traps  may  be  set  without  bait 
in  the  entrances  to  the  burrows,  or,  baited  with  rolled  barley,  set  in 
the  squirrel  paths,  or  near  the  places  where  the  squirrels  are  feeding. 
In  any  case  it  is  well  to  scrape  out  by  a  shove  of  the  foot  a  slight 


11 


Fig.  3. — Sectional  view  of  squirrel  "Destructor."  (Drawing  from  blueprint 
furnished  by  United  States  Public  Health  Service.)  1,  air  cylinder;  2,  bisulphide 
tank;  3,  filler;  4,  vaporizing  chamber;  5,  veneer  wood  circles;  6,  air  space  to  lower 
valves;  7,  inlet  air  valves;  8,  outlet  air  valves;  9,  air  shaft;  10,  piston  head;  11, 
piston  rod;  12,  lock  nuts;  13,  cup  leather  packing;  14,  handle;  15,  measuring  cup; 
16,  three-way  cock;  17,  hose  outlet;  18,  air  inlet  to  vaporizing  chamber;  19,  foot 
rest;  20,  air  vent  in  measuring  cup;   21,  air  deflector;   22,  bottom  board. 


12 


depression  in  which  to  place  the  trap,  so  that  when  set,  the  upper 
surface  of  each  trap  will  be  flush  with  the  surface  of  the  surrounding 
ground.  The  traps  should  be  well  secured  and  this  is  conveniently 
done  by  passing  a  three-foot  lath  sharpened  at  one  end  through  the 
ring  in  the  end  of  the  chain,  and  then  driving  the  lath  well  into  the 
ground.  It  will  serve  also  as  a  marker,  enabling  one  readily  to  find 
the  trap. 

(5)  ENCOURAGEMENT  OF  THE  NATUEAL  ENEMIES  OF  THE 
GROUND  SQUIRREL 
The  killing-off  of  the  natural  enemies  of  the  ground  squirrel  de- 
stroys Nature's  most  effective  check  on  these  destructive  rodents. 
Some  of  these  age-long  natural  enemies  of  the  squirrel  are :  coyotes, 
badgers,  weasels  and  wildcats,  among  mammals;  rattlesnakes  and 
gopher  snakes,  among  reptiles;  red-tailed  hawks  and  golden  eagles, 
among  birds.  Badgers,  weasels  and  snakes  capture  the  ground  squir- 
rels in  their  burrows.  Wildcats  and  coyotes  lie  in  wait  near  the 
burrows  untij.  the  squirrels  venture  forth  in  search  of  food,  when 
they  pounce  upon  them.  Hawks  and  eagles  swoop  down  on  the 
squirrels  .from  their  vantage  points  in  the  air.  The  fact  that  there 
are  so  many  and  varied  natural  checks  on  the  ground  squirrel  shows 
the  necessity  of  preserving  as  many  of  these  native  enemies  as  possible, 
if  the  prolific  squirrel  is  to  be  kept  within  bounds.  The  aid  of  coyotes, 
wildcats  and  rattlesnakes  may  well  be  dispensed  with ;  but  badgers, 
gopher  snakes,  hawks  and  eagles  cost  us  little  or  nothing  to  let  alone ; 
and  each  one  of  these  animals  is  catching  ground  squirrels  almost 
throughout  its  lifetime.  The  following  observations  by  James  B. 
Dixon  show  what  certain  hawks  and  eagles  actually  accomplish  in 
destroying  ground  squirrels.  The  dead  squirrels  counted  in  the  nests 
cited  represent  merely  the  surplus  which  the  old  birds  had  carried  to 
the  young.  The  squirrels  that  the  old  birds  or  the  young  may  have 
eaten  on  the  day  of  observation  are  not  taken  into  account. 


Destructive  Rodents  Found  in  Nests  of  Hawks  and  Golden  Eagle  in 


San  Diego  County 

Species  of  bird                  D 

ate 

Young-  and  eggs 

Locality 

Evidence 

Red-bellied   Hawk     Apr. 

3 

1916 

3    young,    1    week 
old,    and    1    rot- 
ten egg 

Pala 

1  ground  squirrel 
and   2   gophers 

Western  Red-tailed  Mar. 

28, 

1906 

1  day-old  chick,  2 

Vista 

remains    of    2 

Hawk 

pipped  eggs  and 
1  rotten  egg 

ground  squirrels 

Golden  Eagle              Mar. 

26, 

1909 

1  day-old  chick 

Rincon 

9  jack  rabbits 

Golden  Eagle              Apr. 

4, 

1907 

2    young,    1    week 
old 

Lilac 

1  1  ground  squirrels 
in  and  about  nest 

13 

OTHER  METHODS  OF  CONTROL 

Many  small  deciduous  orchards  are  to  be  found  more  or  less 
isolated  in  foothill  regions  in  different  parts  of  the  state.  Squirrel 
depredations  in  such  orchards  can  often  be  prevented  by  tacking 
smooth  pieces  of  tin  about  the  tree  trunks.  If  the  tinning  is  started 
about  two  feet  above  the  ground  and  continued  upwards  for  two  or 
three  feet  it  will  usually  keep  the  ground  squirrels  out  of  the  trees 
unless  there  are  drooping  branches  which  they  can  climb. 

Seed  corn  has  been  protected  from  ground  squirrels  during  germin- 
ation by  being  treated  with  coal  tar.5  Add  one  large  spoonful  of  coal 
tar  to  a  gallon  of  boiling  water.  When  the  mixture  has  cooled  some- 
what the  corn  may  be  stirred  in  and  allowed  to  remain  several  minutes 
without  danger  to  germination. 


SOME    DIFFICULTIES    IN    GROUND    SQUIRREL    CONTROL 

One  of  the  most  discouraging  features  in  the  work  of  ground 
squirrel  control  is  the  indifferent,  "do-nothing,"  attitude  of  a  few 
people  in  each  locality  who  make  just  as  little  effort  as  the  law  allows, 
to  rid  their  land  of  these  pests.  Many  conscientious  and  progressive 
ranchers  have  justly  demanded  to  know  why  they  should  continue 
to  rid  their  fields  of  ground  squirrels  when  previous  experience  has 
shown  that,  when  cleaned  up,  these  fields  have  been  promptly  restocked 
from  the  squirrel-infested  lands  of  their  negligent  neighbors.  Now 
that  we  have  an  adequate  squirrel-eradication  law,  there  should  be 
less  cause  for  complaint  on  this  score. 

There  is  no  question  but  that  the  most  effective  campaign  against 
ground  squirrels  is  one  in  which  the  whole  community  joins.  Co- 
operation in  this  work  is  the  only  way  in  which  all  the  ground  can 
be  covered,  and  co-operation  is  therefore  essential  to  success.  The 
cost  of  the  war  on  ground  squirrels  can  be  materially  reduced  by  a 
community  purchasing  strychnine  and  carbon  bisulphide  in  wholesale 
quantities.  One  of  the  most  successful  co-operative  efforts  along  this 
line  in  California  was  conducted  as  follows.  A  local  ordinance  com- 
pelling action  in  cleaning  up  infested  land  was  secured.  The  squirrel 
inspector  then  worked  in  co-operation  with  the  Farm  Bureau,  and 
barley  and  strychnine  were  purchased  in  quantities  under  the  direc- 
tion of  the  Farm  Advisor.  The  best  known  formula  was  used  in 
making  the  poisoned  grain,  which  was  then  packed  in  five-gallon 
wooden  containers  and  shipped  to  central  distributing  points.  Here 
it  was  sold  at  cost,  which  was  at  that  time  $2  per  container.     A  copy 


5  Lantz,  D.  E.     U.  S.  Dept,  Agric.  Yearbook,  Separate  no.  708,  1916,  p.  7. 


14 

of  the  formula  used,  with  directions  for  administering  an  antidote 
for  the  poison,  was  pasted  on  the  containers,  together  with  the  label 
''Farm  Bureau  Squirrel  Poison."  This  system  insured  a  supply 
of  uniform,  effective,  and  reliable  poisoned  grain  for  the  people's 
use  at  the  lowest  current  price. 

BOUNTY   SYSTEM   A   FAILURE 

Some  variety  of  bounty  system  intended  to  secure  the  eradication 
of  injurious  rodents  such  as  the  ground  squirrel  has  been  tried,  in 
Tulare  and  in  other  counties  in  California,  but  in  most  cases  has 
proved  far  from  satisfactory.  Such  a  system  usually  results  in  an 
early  depletion  of  the  funds  provided  to  pay  the  bounty,  after  which 
the  animals  are  soon  permitted  to  regain  their  former  numbers. 
Bounties  have  not  resulted  in  extermination  of  the  animals  aimed 
at  in  any  of  the  several  states  where  tried.  A  bounty  high  enough 
to  secure  extermination  would  be  prohibitive  on  account  of  the  cost, 
as  no  state  or  county  could  stand  the  financial  strain  for  any  great 
length  of  time.  A  lower  bounty  means  that  the  animals  will  be 
trapped  only  so  long  as  it  is  profitable,  after  which  they  will  be  left 
to  breed  up  again.  L.  B.  Nagler,  Assistant  Secretary  of  State  in 
Wisconsin,  says:0  "I  have  had  ten  years'  experience  in  auditing 
bounty  claims,  and  the  results  convince  me  that  the  system  in  vogue 
is  not  only  ineffective,  but  wasteful,  and,  in  a  large  measure,  harmful. ' ' 

It  is  the  opinion  of  those  best  informed  on  the  subject,  that  the 
bounty  system  is  not  only  vastly  expensive  and  productive  of  endless 
fraud,  but  that  it  fails  to  accomplish  the  end  desired. 


Fins,  Feathers  and  Fur,  June,  1917,  p.  1. 


STATION  PUBLICATIONS   AVAILABLE   FOR   FREE   DISTRIBUTION 


REPORTS 

1897.      Resistant  Vines,   their  Selection,   Adaptation,   and  Grafting.      Appendix  to  Viticultural 
Report  for  1896. 

1902.  Report  of  the  Agricultural   Experiment   Station  for   1898-1901. 

1903.  Report  of  the  Agricultural   Experiment  Station  for   1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment   Station  for   1903-04. 

1914.  Report  of  the  College  of  Agriculture  and  the  Agricultural   Experiment  Station,   Julv, 

1913-June,    1914. 

1915.  Report  of  the  College  of  Agriculture  and  the  Agricultural  Experiment  Station,   Julv, 

1914-June,    1915. 

1916.  Report  of  the  College  of  Agriculture   and  the  Agricultural   Experiment   Station,   July, 

1915-June,    1916. 

1917.  Report  of  the   College  of  Agriculture   and   the    Agricultural    Experiment    Station,    July, 

1916 — June,    1917. 


No. 

230. 
241. 
242. 
246. 
248. 

249. 
250. 
251. 


252. 
253. 

255. 
257. 
261. 

262. 

263. 
264. 
265. 
266. 

267. 
268. 


No. 
113. 
114. 
115. 
121. 

124. 
126. 
127. 
128. 
129. 
131. 
133. 
134. 
135. 
136. 
137. 
138. 
139. 


140. 

141. 

142. 

143. 

144. 
145. 

147. 
148. 
150. 
151 


BULLETINS 

No. 

Enological  Investigations.  270. 

Vine  Pruning  in  California,  Part  I. 

Humus  in  California  Soils. 

Vine  Pruning  in  California,  Part  II.  271. 

The  Economic  Value  of  Pacific  Coast  272. 

Kelps.  273. 
Stock-Poisoning  Plants  of  California. 

The  Loquat.    •  274. 
Utilization  of  the  Nitrogen  and  Organic 

Matter   in    Septic    and    Imhoff    Tank  275. 

Sludges. 

Deterioration  of  Lumber.  276. 

Irrigation   and   Soil   Conditions   in   the  277. 

Sierra  Nevada  Foothills,  California.  278. 

The  Citricola    Scale.  279. 

New  Dosage  Tables.  280. 
Melaxuma    of    the    Walnut,    "Juglans 

regia."  281. 
Citrus   Diseases   of  Florida   and   Cuba 

Compared  with  Those  of  California.  282. 
Size  Grade  for  Ripe  Olives. 

The  Calibration  of  the  Leakage  Meter.  283. 

Cotton  Rot  of  Lemons  in  California.  284. 

A  Spotting  of  Citrus  Fmits  Due  to  the  285. 

Action  of  Oil  Liberated  from  the  Rind.  286. 

Experiments  with  Stocks  for  Citrus.  287. 
Growing  and  Grafting  Olive  Seedlings. 

CIRCULARS 


Correspondence  Courses  in  Agriculture. 

Increasing  the  Dutv  of  Water. 

Grafting  Vinifera  Vineyards. 

Some  Things  the  Prospective  Settler 
Should  Know. 

Alfalfa   Silage  for  Fattening  Steers. 

Spraying  for  the  Grape  Leaf  Hopper. 

House  Fumigation. 

Insecticide  Formulas. 

The  Control  of  Citrus  Insects. 

Spraying  for  Control  of  Walnut  Aphis. 

Countv   Farm   Adviser. 

Control  of  Raisin   Insects. 

Official  Tests  of  Dairy  Cows. 

Melilotus  Indica. 

Wood  Decay  in   Orchard  Trees. 

The  Silo  in  California  Agriculture. 

The  Generation  of  Hydrocyanic  Acid 
Gas  in  Fumigation  by  Portable  Ma- 
chines. 

The  Practical  Application  of  Improved 
Methods  of  Fermentation  in  Califor- 
nia Wineries  during  1913  and  1914. 

Standard  Insecticides  and  Fungicides 
versus  Secret  Preparations. 

Practical  and  Inexpensive  Poultrv  Ap- 
pliances. 

Control  of  Grasshoppers  in  Imperial 
Valley. 

Oidium  or  Powder'-  Mildew  of  the  Vine 

SuErcrostions  to  Poultrvmon  concerning 
Chicken  Pox. 

Tomato   Growing  in   California. 

"Lnngworms." 

Round   Worms   in    Poultrv. 

Feeding  and   Management   of   Hogs. 


No. 
152. 

153. 

154. 

155. 
156. 
157. 
158. 
160. 
161. 
162. 

164. 
165. 

166. 
167. 
168. 

169. 
170. 

171. 
Ml. 
173. 

174. 
175. 


177. 
178. 


A  Comparison  of  Annual  Cropping,  Bi- 
ennial Cropping,  and  Green  Manures 
on  the  Yield  of  Wheat. 

Feeding  Dairy  Calves  in  California. 

Commercial  Fertilizers. 

Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain. 

The  Common  Honey  Bee  as  an  Agent 
in   Prune   Pollination. 

The  Cultivation  of  Belladonna  in  Cali- 
fornia. 

The  Pomegranate. 

Sudan  Grass. 

Grain  Sorghums. 

Irrigation  of  Rice  in  California. 

Irrigation  of  Alfalfa  in  the  Sacramento 
Valley. 

Control  of  the  Pocket  Gophers  in  Cali- 
fornia. 

Trials  with  California  Silage  Crops  for 
Dairy  Cows. 

The  Olive  Insects  of  California. 

Irrigation  of  Alfalfa  in  Imperial  Valley. 

The  Milch  Goat  in  California. 

Commercial  Fertilizers. 

Vinegar  from  Waste  Fruits. 


Some  Observations  on  the  Bulk  Hand- 
ling of  Grain  in  California. 
Announcement  of  the  California  State 

Dairv  Cow  Competition,    1916-18. 
Irrigation    Practice  in   Growing   Small 

Fruits  in  California. 
Rovine  Tuberculosis. 
How  to  Operate  an  Incubator. 
Control  of  the  Pear  Scab. 
Home  and  Farm  Canning. 
Lettuce    Growing   in    California. 
Potatoes  in   California. 
White    Diarrhoea    and    Coccidiosis    of 

Chicks. 
Small  Fruit  Culture  in  California. 
Fundamentals    of    Sugar    Beet    under 

California  Conditions. 
The  County  Farm  Bureau. 
Feeding  Stuffs  of  Minor  Importance. 
Spraying  for  the  Control  of  Wild  Morn 

ing-Glory  within  the  Fog  Belt. 
1918  Grain   Crop. 
Fertilizing  California  Soils  for  the  1918 

Crop. 
Th^  Fertilization  of  Citrus. 
Wheat  Culture. 
The    Construction    of    the    Wood-Hoop 

Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the  Marketing  and 

Distribution    of    Milk. 
Hog      Ohnlora      Prevention      and      the 

Serum    Treatment. 
Oraip    Sorehnm    Seed. 
The    Packing   of   Apples   in    California. 


